Leucine transport from the ventricles and the cranial subarachnoid space in the cat

Abstract— The clearance of [¹⁴C]leucine from the ventricular and cranial subarachnoid space was studied in cats subjected to ventriculo-cisternal and ventriculo-craniosubarachnoidal perfusions. Clearance from both the ventricles and the subarachnoid space was mediated by transport mechanisms with nonsaturable and saturable components. Net clearance from the subarachnoid space was considerably greater than from the ventricles. Analysis of the transport kinetics revealed the affinity constants (K_t) to be comparable for both compartments but transport sites appeared to be more numerous in the subarachnoid space (greater V_max). Proportionally, the amount of [¹⁴C]leucine retained by brain declined as the concentration of leucine in the perfusate was increased. Since at high concentrations the CSF transport systems and presumably cellular uptake were inhibited (self-saturated) it was assumed that the lower brain levels of [¹⁴C]leucine reflected a proportionately greater loss of [¹⁴C]-leucine from the brain interstitial space to blood.